Two parts to this post. The first part informational.

I've started rewiring the living room which involves getting rid of
the two surface mounted double sockets and replacing with 8 doubles.
(I'm pretty sure I understood the OSG correctly where it recommends 6
double sockets for a room of its size plus an extra two doubles for
"home entertainment areas"!).

After spending a long time reading the pros and cons of various ways
of chasing out socket boxes I settled on an Armeg SDS Scutch Comb
chisel from Screwfix £29.59

http://tinyurl.com/2w97xl3

I carefully marked out the perimeter of the cut with a pencil, then
scored round with a Stanley knife, then delicately took off the skim
coat with the Armeg chisel. I did attempt to "stitch drill" the
perimeter first, but realised after the first box that this was not
necessary. Once through the skim coat I went hard at it with the
Armeg, down to the brick. Then I gradually ground away at the brick
until the hole was the correct depth.

This was my first attempt at cutting out socket boxes and I was pretty
pleased with the end result. I am sure a pro would have cracked them
out a fair bit quicker than me but it was a neat job. Compared to the
flat SDS chisel bit I tried at first, the comb was far better, as the
"teeth" dig into the wall meaning the bit doesn't skate about all over
the place.

I also used this tool during my gas meter box installation (see other
post!), again, excellent for finishing off and tidying up.

Okay, onto the second part of my post, and probably a pretty dim
question, but I now have to run chases to the floor for my new socket
boxes. I will be fitting oval conduit to carry the 2.5mm2 T+E cable to
the floor void. Is it normal to use two parrallel chases or one thick
one carrying both cables? And depending on the choice, what size oval
conduit is recommended? I see it comes in 13, 16, 22 and 29mm sizes.

I have baffled myself with grouping factors from the OSG and have come
to the (hopefully correct!) conclusion that I can pretty much
disregard this as the grouped cables will only be 6" lengths.

Thanks in advance, sorry for the long post!

Luke

Luke wrote:
Two parts to this post. The first part informational.

After spending a long time reading the pros and cons of various ways
of chasing out socket boxes I settled on an Armeg SDS Scutch Comb
chisel from Screwfix £29.59

http://tinyurl.com/2w97xl3

I carefully marked out the perimeter of the cut with a pencil, then
scored round with a Stanley knife, then delicately took off the skim
coat with the Armeg chisel. I did attempt to "stitch drill" the
perimeter first, but realised after the first box that this was not
necessary. Once through the skim coat I went hard at it with the
Armeg, down to the brick. Then I gradually ground away at the brick
until the hole was the correct depth.

This was my first attempt at cutting out socket boxes and I was pretty
pleased with the end result. I am sure a pro would have cracked them
out a fair bit quicker than me but it was a neat job. Compared to the
flat SDS chisel bit I tried at first, the comb was far better, as the
"teeth" dig into the wall meaning the bit doesn't skate about all over
the place.

I also used this tool during my gas meter box installation (see other
post!), again, excellent for finishing off and tidying up.

Okay, onto the second part of my post, and probably a pretty dim
question, but I now have to run chases to the floor for my new socket
boxes. I will be fitting oval conduit to carry the 2.5mm2 T+E cable to
the floor void. Is it normal to use two parrallel chases or one thick
one carrying both cables? And depending on the choice, what size oval
conduit is recommended? I see it comes in 13, 16, 22 and 29mm sizes.

I have baffled myself with grouping factors from the OSG and have come
to the (hopefully correct!) conclusion that I can pretty much
disregard this as the grouped cables will only be 6" lengths.

Thanks in advance, sorry for the long post!

Luke

I am glad you used enjoyed the Armeg Scutch comb.

As for your plan to drop the 2.5 t&E through conduit to under the
floorboards then I see no problem. You can use either one conduit or two in
parrallel, use whichever method you want or can easily get the cables
through. Getting 2x2.5 T&E cables through 22mm is possible.

There is no grouping factor to apply as there is only one circuit in volved.
There are cable capacities to consider for long lengths of conduit runs but
not for the job you are considering.

Cheers

Adam

On 1 Aug, 10:57, "ARWadsworth" wrote:

Getting 2x2.5 T&E cables through 22mm [oval conduit] is possible.

What would your rule of thumb be for round plastic conduit? 20mm or
25mm? Is it either possible, or practical (i.e. not a stupid amount
of hassle) to pull 2×2.5mm^2 for a ring circuit through 20mm, or is it
better to go to 25mm.

Andy Dingley wrote:
On 1 Aug, 10:57, "ARWadsworth" wrote:

Getting 2x2.5 T&E cables through 22mm [oval conduit] is possible.

What would your rule of thumb be for round plastic conduit? 20mm or
25mm? Is it either possible, or practical (i.e. not a stupid amount
of hassle) to pull 2×2.5mm^2 for a ring circuit through 20mm, or is it
better to go to 25mm.


I would not attempt to pull 2x 2.5T&Es through 20mm round conduit apart from
on short straight lengths. Anything longer than a couple of metres and it
becomes a hassle. If all the ring is in conduit then I would use singles not
T&E.

Cheers

Adam

Andy Dingley wrote:

Is it either possible, or practical (i.e. not a stupid amount
of hassle) to pull 2×2.5mm^2 for a ring circuit through 20mm, or is it
better to go to 25mm.

I found getting a 2.5mm^2 2&E together with a 1.5mm^2 3&E through 20mm
round plastic was "fun".

ARWadsworth wrote:
Andy Dingley wrote:
On 1 Aug, 10:57, "ARWadsworth" wrote:

Getting 2x2.5 T&E cables through 22mm [oval conduit] is possible.
What would your rule of thumb be for round plastic conduit? 20mm or
25mm? Is it either possible, or practical (i.e. not a stupid amount
of hassle) to pull 2×2.5mm^2 for a ring circuit through 20mm, or is it
better to go to 25mm.


I would not attempt to pull 2x 2.5T&Es through 20mm round conduit apart from
on short straight lengths. Anything longer than a couple of metres and it
becomes a hassle. If all the ring is in conduit then I would use singles not
T&E.

This answers a question I have concerning a job I have coming up where
I'd like to use conduit! Is it possible to buy single-core cable in
lengths of less than 100m? I probably only need 10-20m, and am unlikely
to ever need it to use it again after this...

(wonder if I could just take a Stanley knife to the roll of 2.5mm T&E I
have in the garage!!)

David

Lobster wrote:

Is it possible to buy single-core cable in
lengths of less than 100m? I probably only need 10-20m, and am unlikely
to ever need it to use it again after this...

Cut lengths from a wholesaler?

(wonder if I could just take a Stanley knife to the roll of 2.5mm T&E I
have in the garage!!)

But that would only be single insulated, unlike proper BS6491X cable.

"Andy Burns" wrote in message
...
Lobster wrote:

Is it possible to buy single-core cable in
lengths of less than 100m? I probably only need 10-20m, and am unlikely
to ever need it to use it again after this...

Cut lengths from a wholesaler?

(wonder if I could just take a Stanley knife to the roll of 2.5mm T&E I
have in the garage!!)

But that would only be single insulated, unlike proper BS6491X cable.

BS6491X cable is the single insulated cable (and is stranded to allow it to
be pulled through conduit). The double insulated cable is 6181Y.

Cheers

Adam

ARWadsworth wrote:

BS6491X cable is the single insulated cable (and is stranded to allow it to
be pulled through conduit). The double insulated cable is 6181Y.

Thanks for the correction.

Andy Dingley wrote:
On 1 Aug, 10:57, "ARWadsworth" wrote:

Getting 2x2.5 T&E cables through 22mm [oval conduit] is possible.

What would your rule of thumb be for round plastic conduit? 20mm or
25mm? Is it either possible, or practical (i.e. not a stupid amount
of hassle) to pull 2×2.5mm^2 for a ring circuit through 20mm, or is it
better to go to 25mm.

You could ask Tim Watts about his experiences of mixing T&E with conduit. He
used conduit for the vertical drops behind the plaster but I am sure that he
used T&E as the cables went on a cable tray in the loft. I think he used
25mm conduit and he never tried to squeeze two cables down the same piece of
conduit.

--
Adam

Andy Burns wrote:
Lobster wrote:

Is it possible to buy single-core cable in
lengths of less than 100m? I probably only need 10-20m, and am unlikely
to ever need it to use it again after this...

Cut lengths from a wholesaler?

(wonder if I could just take a Stanley knife to the roll of 2.5mm T&E I
have in the garage!!)

But that would only be single insulated, unlike proper BS6491X cable.

Ah OK, I wasn't entirely serious but good to know!

Incidentally, if you're running 2.5mm singles, is 2.5mm green/yellow
sleeved cable the correct one to use for the CPC (bearing in mind that
in ordinary T&E the CPC is smaller than the L/N cables)?

Thanks
David

Lobster wrote:
ARWadsworth wrote:
Andy Dingley wrote:
On 1 Aug, 10:57, "ARWadsworth" wrote:

Getting 2x2.5 T&E cables through 22mm [oval conduit] is possible.
What would your rule of thumb be for round plastic conduit? 20mm or
25mm? Is it either possible, or practical (i.e. not a stupid amount
of hassle) to pull 2×2.5mm^2 for a ring circuit through 20mm, or is it
better to go to 25mm.


I would not attempt to pull 2x 2.5T&Es through 20mm round conduit
apart from on short straight lengths. Anything longer than a couple of
metres and it becomes a hassle. If all the ring is in conduit then I
would use singles not T&E.

This answers a question I have concerning a job I have coming up where
I'd like to use conduit! Is it possible to buy single-core cable in
lengths of less than 100m? I probably only need 10-20m, and am unlikely
to ever need it to use it again after this...

(wonder if I could just take a Stanley knife to the roll of 2.5mm T&E I
have in the garage!!)

David
You could do the Stanley knife trick but it would yield solid copper
cable and so less flexible than the proper stranded conduit cable.
Depends on how many bends to have to contend with or if you can thread
the cables through as you add the bends/constrictions which would sound
feasible for 10-20m total run.

Bob

If you can go around the room horizontally you can use 20mm conduit
with 6491X singles.
Cut lengths of Br Bl Gr/Ye 6491X can be bought from www.tradingdepot.co.uk
for 20p (2.5mm) & 12p (1.5mm) per metre, but they do not list 4mm
which is annoying re 30A radial & 4mm Gr/Ye is useful for "no-
mechanical protection" re bonding.

If you have a wooden floor I would just use FTE and go under the
floor, around the room or drop from the ceiling void above as
necessary.

If you are using vertical cable entry (top/bottom) then I would use
one for cable entry and one for cable exit. It only means a little
more work, but makes things more flexible in future. The ideal is
always 20mm round conduit if your plaster depth is already at the 20mm
level so little excavation required - although 28mm oval with a 25mm
hole is "spacious" too.

Use 35mm backboxes, that way you can have a good loop of cable inside
for repairs if you do not oval and general wiring space for any future
changes. Can be worth adding 1-2 other boxes with separate oval/
conduit even with blank plates for BT or network or anything.

Lobster wrote:
Andy Burns wrote:
Lobster wrote:

Is it possible to buy single-core cable in
lengths of less than 100m? I probably only need 10-20m, and am
unlikely to ever need it to use it again after this...

Cut lengths from a wholesaler?

(wonder if I could just take a Stanley knife to the roll of 2.5mm
T&E I have in the garage!!)

But that would only be single insulated, unlike proper BS6491X cable.

Ah OK, I wasn't entirely serious but good to know!

Incidentally, if you're running 2.5mm singles, is 2.5mm green/yellow
sleeved cable the correct one to use for the CPC (bearing in mind that
in ordinary T&E the CPC is smaller than the L/N cables)?

Thanks
David

There is no reason to run a 2.5mm green/yellow in most cases.

You will not need one for a 20m long ring. 1.5mm cpc will be OK.
--
Adam